U.S. Border Patrol ranch liaison John "Cody" Jackson, right, rides with cattle rancher Dan Bell at the U.S.-Mexico border on March 8 in Nogales, Ariz. / John Moore, Getty Images

by Alan Gomez, USA TODAY

by Alan Gomez, USA TODAY

Though many in Washington have been hailing the recent progress made on a sweeping immigration bill that would legalize the nation's estimated 11million illegal immigrants, major disagreements over how best to secure the nation's Southwest border with Mexico threaten to derail the process.

Lawmakers in the nation's capital are largely in agreement that the border must be secured, but the next battle will be how to secure it - and over what time period. A failure to find common ground on this critical issue could be enough to snuff out a compromise, and with it the first comprehensive immigration legislation in more than a quarter-century.

"I wouldn't vote for the president's fast-track, and I wouldn't vote for the Senate's slower track," said Rep. John Carter, R-Texas, a member of a bipartisan group of House members drafting a House immigration plan. "I think there's a better way to do it."

That "fast track" is President Obama's argument that illegal immigrants need a path to legal status now and should not wait until the border is secured. In the Senate, a bipartisan group of senators - the "Gang of Eight" - is trying to craft a provision in their bill that could quantify and establish a level of border security that must be reached before illegal immigrants can apply for legal residency and U.S. citizenship.

Though many congressional Republicans understand the political reality that the party needs to remake its image with Latinos after the 2012 election, the pall from the last major immigration law still hangs over today's negotiations. That landmark bill, signed in 1986 by President Reagan, was sold as a solution to illegal immigration and a way to secure the border. The citizenship part happened; the border part did not. Millions of people from Mexico and other parts of Latin America have continued to enter illegally through a porous Southwest border, and others who entered the country legally have continued overstaying their visas.

"The amnesty provisions become law, they become final ... and the promises of enforcement don't occur. I really believe that is a danger again," Sen. Jeff Sessions, R-Ala., said in February on the Senate floor, echoing a fear among many of the party faithful.

Republicans backed the 1986 bill that granted amnesty to an estimated 3 million illegal immigrants. The legislation was coupled with a vow to close illegal border crossings and crack down on the hiring of these immigrants, neither of which occurred. Now the GOP demands the border be secured for good before agreeing to citizenship for those who are here.

Some senators were excited to clear one roadblock to a deal this past weekend when the AFL-CIO, the nation's largest coalition of labor unions, and the U.S. Chamber of Commerce, agreed to support giving up to 200,000 visas a year to foreigners for janitorial, hospitality and construction work. But that agreement would go nowhere if a deal on security cannot be reached.

GETTING BUY-IN

Sen. Marco Rubio of Florida, a rising GOP star viewed as a possible 2016 presidential contender, was the Gang of Eight member chosen to sell the immigration plan to several conservative media outlets. During one appearance, radio host Rush Limbaugh told Rubio that many listeners were worried the Senate group wouldn't take border security seriously.

"If it doesn't, then I'll come back to you and say, 'Look, it didn't. We tried,'" Rubio responded during the January interview.

There is disagreement over how one shuts down a border stretching 1,969 miles across desert, mountain passes and the Rio Grande. Some sheriffs along the border say the answer is more "boots on the ground," or border guards blocking those who try to make the trek despite the odds.

In fact, the federal government boosted the number of Border Patrol agents from just over 4,000 in 1993 to more than 21,000 in 2012. That increase, as well as the economic recession that eliminated many of the jobs luring so many illegal immigrants, led to sharp drops in crossings. More than 1 million people a year crossed the border illegally from 2004-06. By 2012, that number was 364,000.

Sheriff Paul Babeu of Arizona's Pinal County says more boots is only part of the answer. Babeu previously commanded a unit of Army National Guard troops who patrolled the border and is now sheriff of an inland county that is a major channel for human and drug smuggling. His solution to seal the border: Add 6,000 border agents and National Guardsmen, build more fencing and rigorously enforce existing laws. "You can get close to that, yes," he said.

Others along the border say the strategy, not the number, of federal agents there needs to change.

Donald Reay, executive director of the Texas Border Sheriff's Coalition - which includes the chief law enforcement officer of all Texas counties within 25 miles of the border - said Border Patrol agents in his state often work miles inland, focusing on high-volume immigration corridors rather than patrolling the border itself. That leads many ranchers and farmers who live along the border to say they live in "almost America."

"They're not seeing Border Patrol on a regular basis," Reay said. "That's a decision that's made in Washington. It's hard for us to tell another agency, 'You're doing your job wrong.' But our sheriffs have to try to fill that gap. And quite frankly, we don't have the manpower to do that."

Sen. Charles Schumer, D-N.Y., and Sen. John McCain, R-Ariz., both in the Gang of Eight, toured the Arizona border last Wednesday and watched as a woman scaled an 18-foot-high border fence in Nogales. Both said Border Patrol needs more technological assistance to fill in gaps.

Though agents already use cameras, sensors and drones to monitor people crossing the border, those technologies need to be augmented, Schumer said.

"We have adequate manpower, but not adequate technology," he said after the tour.

BIGGER THAN THE BORDER

Former Homeland Security secretary Michael Chertoff said Congress also needs to figure out how to identify "visa overstays" - about 40% of illegal immigrants entered the country legally with a visa but stayed after it expired. At least two of the 9/11 hijackers were in the U.S. after overstaying tourist visas. Chertoff also said little has been done to monitor people who enter illegally by water.

He said focusing solely on the Southwest border "would be like if you have three doors to your house and you only lock one. This popular image of people running across the deserts or the mountains only accounts for a percentage of the total issue," he said.

Others say the problem of illegal crossings will fade away when the country reforms its legal immigration system.

El Paso County Judge Veronica Escobar says the U.S. government has approached the problem of illegal immigration in a "completely backward way." She said most people illegally enter the country to work, so reforming the nation's visa system to allow more foreign workers in temporarily would slow illegal crossings. That would then allow the government to concentrate law enforcement efforts on illegal immigrants who might pose a true threat to national security.

Though that might sound simple enough, just defining what security means has become a point of contention in negotiations.

For years, the Department of Homeland Security relied on a measurement called "operational control" of the border, which Congress defined in 2006 as "the prevention of all unlawful entries into the United States, including entries by terrorists, other unlawful aliens, instruments of terrorism, narcotics and contraband." In 2007, Border Patrol defined operational control as "the ability to detect, respond and interdict border penetrations in areas deemed as high priority for threat potential or other national security objectives."

In 2010, Border Patrol estimated it had established operational control of 873 miles of the border, or 44%. The next year, DHS Secretary Janet Napolitano said the agency was scrapping operational control as a metric and would develop a new measurement for border security: the "border condition index."

Now, DHS says that metric may not be a viable way to truly explain how secure the border is.

'A DIFFICULT LIFT'

During a March 20 House committee hearing, DHS said its agents were using a wide variety of metrics - including apprehensions of people along the border, economic measurements and hotel vacancy rates on the Mexican side of the border - to help them figure out where they need to concentrate efforts. But department officials cautioned it might not be possible to use such a metric as a final grade on overall border security.

That reaction upset House Republicans who had been waiting for years for the new measurement.

"We have a moment in time here," said Rep. Candice Miller, R-Mich., chair of the House Homeland Security subcommittee on Border and Maritime Security. "If we do not as a nation have a high degree of confidence that we are securing our border, or are on the path to measuring border security in a way that we feel confident in, I think this whole comprehensive immigration reform is going to be a very difficult lift."